It is very important to utilize sunlight which is a permanent and stable energy source in considering an energy countermeasure. Photosynthesis by plants is an excellent system capable of transforming sunlight energy to chemical energy most efficiently, and absorbs and assimilates carbon dioxide and excess nutrient salts in the environment. In addition, oxygen is emitted. The development of a technique utilizing plants is therefore expected as a solution for the energy problems.
Among plants, algae live in both of seawater and freshwater that abundantly exist, and are huge in amount. In addition, algae have a significant photosynthesis ability. Further, some of algae produce a useful compound such as unsaturated fatty acid and anti-tumor compound. Furthermore, since some of diatoms produce a useful inorganic substance, a technique called as biomineralization by diatoms is focused. As described above, algae can be said to be important organisms as useful resources.
When an organism is utilized industrially, a transformation technique for introducing a useful gene is generally used. The transformation technique is also used for knocking out a specific gene or preventing the action thereof in order to elucidate the function of the gene.
The transformation of algae, especially diatoms and green algae, has been conventionally carried out. In such a conventional method, an endogenous promoter is separated, a gene is conjugated with the promoter, and the promoter is introduced into algae. However, this method is far from efficient, since a lot of effort and time is required, for separating an endogenous promoter. There is also a problem that the transformation efficiency of algae, particularly of marine algae, is originally very low.
On the other hand, in transformation of animals or plants other than algae, a promoter derived from a virus rather than an endogenous promoter is generally used. For example, a CaMV35S promoter separated from a cauliflower mosaic virus (CaMV) infecting cruciferous plants is used for transforming a wide range of plants without limited to cruciferous plants. For transformation of an animal cell, a CMV promoter separated from a cytomegalovirus (CMV) and a SV40 promoter separated from a simian virus 40 (SV40) are widely used.
Unlike the above situation, in transformation of algae, there is known little example in which an exogenous virus promoter is used.
For example, Non-patent document 1 discloses an experimental example of transforming a diatom Cycrotela cryptica by using a CaMV35S promoter; however, it is reported that a transformant could not obtained.
Non-patent document 2 discloses that a GUS gene is introduced into a diatom Phaeodactylum tricornutum by using a CMV promoter, a CaMV35S promoter or a Rous sarcoma virus (RSV) promoter; as a result, GUS (β-glucuronidase) was expressed in any cases.
Non-patent document 3 discloses that when a GUS gene is introduced into dinoflagellates Amphidinium or Symbiodinium by using a CaMV35S promoter, GUS was expressed. However, according to another document (Non-patent document 4), there is no report describing that another group succeeds in transformation of dinoflagellates in spite of diligent efforts.